Beijing’s 21 million residents have just suffered through the first-ever “code red” pollution warning. And with winter only beginning, there may be more to come.
That’s because air pollution in Beijing is directly correlated to the time of year. There are other important factors, too, like the region’s topography.Here is an explanation of why the capital city’s air pollution is cyclical. And why it’s made worse by factors other than emissions.
Beijing lies in a plain, far below the elevation of mountains that surround it on one side. That can keep some pollution trapped in the city. It also alters wind and weather patterns.Beijing is at the northwest corner of the North China Plain. The Yanshan Mountains surround the city to the west, north and northeast. Beijing’s topography and location creates a climate described as “warm temperate and semi-humid monsoon.” Beijing’s winter season lasts five months or more. There is not usually much snow, but there is cold. Temperatures routinely fall below 0℃The cold weather means people put on heaters, which creates a higher demand for power. Because around 66 percent of China’s power is generated by coal, more demand for power means more coal burned.This climate means Beijing can sometimes be steamy. Humidity is common during the warmer months, averaging about 77 percent in August. The wetter air keeps pollutants trapped and makes it more difficult to blow away. The water molecules actually condense around pollutants, creating the infamous smoggy haze. Then, there’s Beijing’s “man-made” topography. As the city’s population booms – from 10 million in the 1990s to around 20 million today – more housing is needed. One solution has been to build skyscrapers. But tall buildings can also trap pollutants, preventing winds from blowing them out of the city.
Wind tends to blow into Beijing from three directions: from the east, from the south and from the north.When the wind blows from the east, it draws in clean air from over the ocean. The breezes are pleasant and help clear the air in the city. The worst pollution tends to blow in from the south, from provinces like Hebei, Shanxi and Shandong. Their heavily industrialized cities contribute to the capital’s polluted air.So cleaning the air over Beijing starts outside the city.So Beijing’s pollution problem is part meteorological and part man-made. Cleaning the man-made part will require work well outside the capital’s ring roads.